Power skills are skills that allow the possessing character to gain access to an extraordinary power. These skills can only be taken when you gain the Evolved feat, and a character can only possess a single power skill unless another rule states otherwise;

Example: a character with the Power (empathy) skill can gain access to other power skills after coming into contact with another evolved person.

A character can use power skills as much as he would like as long as he takes the proper action to activate it. A power skill takes an attack action, that provokes an attack of opportunity, to activate unless otherwise stated. A power skills effect is considered an extraordinary ability.
A character can use a power skill only if he is conscious, unless stated otherwise.

If a GM chooses they may make the character gain a power at random, rolling a d% and consulting the table bellow.